Final answer:
Microtubule nucleation requires α-tubulin and β-tubulin subunits to form the hollow cylindrical structure that is essential for various cellular functions.
Step-by-step explanation:
Microtubule nucleation requires the subunits of α-tubulin and β-tubulin to occur. These tubulin monomers polymerize to form dimers, which then assemble into the microtubule structure. Microtubules are dynamic cytoskeletal components that help in numerous cellular processes, including maintaining cell shape, enabling cellular motility, and segregating chromosomes during cell division. Microtubule nucleation often occurs at organizing centers such as centrioles, where tubulin subunits are added to form the microtubule.